Return the hash of snapshot block which is most suitable for being referenced by a new transaction

Parameters:

address : AddressOptional account address. Once specified, the hash of snapshot block referenced by last transaction of the account or afterwards will be returned.

sendblockHash : HashOptional hash of the corresponding request block if a new response transaction is to be created. Once specified, the hash of snapshot block referenced by the request transaction or afterwards will be returned.

If neither is specified, the hash of the snapshot block which is 10 blocks prior to current will be returned.